In a computer disc drive, data is stored on a computer disc in concentric tracks. Before reading or writing data to the tracks, the disc drive must position a head over a desired track. In disc drives with rotary actuators, this involves rotating an actuator arm that supports one or more heads at the end of one or more suspension assemblies. The actuator arm is typically rotated about a pivot point using a voice coil motor.
The voice coil motor includes a wound electrical conductor that is connected to the actuator arm, and two magnets that are positioned on opposite sides of the wound conductor. The magnets are separated from the wound conductor and each other by a spacer. When a current passes through the wound conductor, the current interacts with the magnetic fields produced by the magnets thereby causing the wound conductor to move laterally between the magnets. This causes the actuator arm to pivot around the pivot point so that the position of the head changes.
The heads can also move in response to physical forces applied to the outside of the disc drive. If these forces are large enough, they can cause the head to swing wildly in the drive. To prevent damage to the head during these events, stops are in the disc drive to keep the head from moving past the outer edge of the disc and to keep the head from striking a central hub of the disc. In some disc drives, these stops are placed on the spacers that separate the magnets of the voice coil motor.
To minimize damage to the heads, the stops must limit the deceleration experienced by the heads. In addition, the stops should not cause the actuator arm to bounce a significant distance. Under the prior art, these attributes were attained using an elastomeric material such as rubber or urethane that encircles a steel core of the spacer. In some prior art devices, the elastomeric material is surrounded by a spring material such as a thin sheet of steel or plastic.
Although elastomeric materials provide good energy absorption, they are difficult to make with accurate dimensional control and geometric precision. In particular, the dimensions of these materials are highly temperature dependent. Furthermore, the mechanical properties of these material, such as stiffness and dampening, vary significantly with temperature. In addition, these materials tend to outgas thereby contaminating the interior of the disc drive. As such, a stop/spacer is needed that does not require an elastomeric material.